Infection with a high-risk human papillomavirus (HPV) predisposes a woman to developing cervical cancer, but only a small proportion of infected women actually develop the disease. Thus, the evidence suggests that while HPV infection is a necessary step, additional events are necessary for cancer progression. The elaboration of these cofactors is essential to the understanding of the multistage carcinogenesis process and to the treatment of women at high risk for developing cervical cancers. Evidence of potential cofactors exists. Cervical cancer risk is increased by human herpesvirus (HHV) or human immunodeficiency virus (HIV) infection. In vitro experiments demonstrate that HHV-6 and HIV-1 may be involved in the progression to cervical cancer. Nested pairs of primers from pZVH-14 sequence (molecular clone of HHV-6) were used in PCR to demonstrate the persistence of HHV-6 in infected cervical cells. HHV- 6 infection of normal human cells, HPV-16-immortalized cervical cells, or carcinoma-derived cell lines C4-1 or QGH occurred at an efficiency of 10-20%, as indicated by a series of monoclonal antibodies (p41, p42/38, p180, gp110) 14 days postinfection. HPV-16 or -18 expression in immortal or tumor cells was amplified 2-3x as detected by Northern blot. By interpolation of monoclonal and Northern data, HHV-6 upregulated HPV-16 or -18 expression 10-15x. HHV-6 persisted in an episomal state. Preliminary evidence obtained by PCR analysis or in situ hybridization on histopathology sections indicates that a low proportion of HPV- positive cervical cancers has HHV-6 DNA. An HPV-16 LTR-linked CAT (p16E) containing an SV-40 early promoter was able to be transactivated by pZVB- 70 (molecular clone of HHV-6) or pZVH-14 in HeLa cells. In other experiments transactivation of HIV-1 LTR-linked CAT by pZVB-70 or pZVH-14 and HIV TAT also dramatically increased. The fact that HIV and HPVs share some pathways in their natural histories suggests that their combination may also be associated with progression to cervical carcinoma. Reversal of the malignant state by ribozymes that inactivate HPV E6 oncogenes is currently being investigated.